1. Field
Exemplary embodiments of the present invention relate to a memory and a memory system including the same, and more particularly, to a refresh technology for a memory and a memory system.
2. Description of the Related Art
A memory cell of a memory includes a transistor which functions as a switch and a capacitor for storing charges, that is, a data. The logic level of the data stored in a memory cell may be distinguished between the levels of ‘high’ (logic 1) and ‘low’ (logic 0) according to whether there is a charge in the capacitor of the memory cell, that is, whether the voltage at the end of the capacitor is high or low.
A data may be stored and retained in a memory cell so long as charges are accumulated in a capacitor, thereby consuming no power in principle. However, the data may be lost because the initial amount of charges that are stored in the capacitor may decrease due to leakage current caused in a PN bonding/junction of a metal-oxide semiconductor (MOS) transistor. To prevent the loss of data, the data in the memory cell is read before the data gets lost and the memory cell may be recharged to maintain the initial amount of charges according to the information that is read. This operation is to be repeated periodically to retain the data, and the operation of recharging the memory cell is called a refresh operation.
The refresh operation is performed whenever a refresh command is applied from a memory controller to a memory. The memory controller applies the refresh command to the memory every predetermined time in consideration of the data retention time of the memory. For example, when the data retention time of a memory is 64 ms and all of the memory cells in the memory are refreshed only after the refresh command is applied 8000 times, the memory controller applies the refresh command to the memory 8000 times during the term of 64 ms. When it turns out in a memory test process that the data retention time of some memory cells included in the memory do not exceed a predetermined reference time, the memory is regarded as a defective memory and abandoned.